A conventional fault detection device for an inverter circuit includes: a current measuring unit that measures current of an inverter circuit that drives a motor; an overcurrent determination circuit that determines whether the measured current is overcurrent based on an output signal of the current measuring unit; and an inverter-output control circuit that controls an output of an inverter driving circuit that drives the inverter circuit based on an output signal of the overcurrent determination circuit. Here, current is forcibly supplied to at least one phase of a motor coil before rotationally driving the motor by the inverter circuit, the current is measured by the current measuring unit, the overcurrent determination circuit determines whether the measured current is overcurrent based on the output signal of the current measuring unit, and it is determined whether there is an abnormality based on the output signal of the overcurrent determination circuit (for an example, see Patent Document 1).
In this case, when detection of fault in the inverter circuit is performed, and if the current measuring unit has failed, it is not possible to measure the current of the inverter circuit, and consequently, it is not possible to detect the fault in the inverter circuit. Thus, it is important to detect the fault in the current measuring unit. In this regard, as another fault detection device for an inverter circuit, there is a technique in which plural current measuring units are provided to detect the fault in the current measuring units and currents measured by the respective current measuring units are compared with each other to mutually monitor the fault in the current measuring units.